Vibration related failures in electronic systems are typically caused by high acceleration levels, high stress levels, and large displacement amplitudes. Typically, in electronic assemblies, printed circuit boards (PCBs) are mounted directly to the housing of the electronic assembly, which saves cost and part count. However, it allows for the direct transmission of vibration energy from the housing to the PCB. High acceleration levels at the PCB are driven by direct transmission of energy levels from the surrounding environment. These levels are then amplified by PCB resonance and transmissibility as well as by unsupported large and/or high mass components. Under such conditions, a 20 g RMS input can be amplified to 90 g as a result of PCB resonance for on-engine electronics. Stress levels at the PCB and components increase proportionally with vibration levels. Large displacement amplitudes are directly related to resonance of unsupported PCB spans. Large displacements typically result in higher stress levels at electronic component mountings on the PCB and at locations where the PCB is mounted to the housing.
The transmissibility of a PCB (i.e., the ratio of output acceleration to input acceleration excitation) is generally very high. Typically, the transmissibility is on the order of from 20 to 80, indicating that transmissibility is one of the main causes for failure as a result of vibration in component parts mounted on PCBs. FIG. 7 depicts a conventional PCB assembly 100. As can be seen, two PCBs 102 are suspended on a chassis 104. Fasteners 106 attach the PCBs 102 to standoff mounts 108 on the chassis 104. Thus, the PCBs 102 are directly attached to the chassis 104, and therefore, vibrations from the engine are directly transmitted to the PCBs 102 through the chassis 104.
Various attempts have been made to reduce the transmission of vibrations to PCBs. For instance, some of the prior approaches use potting materials or complicated mechanical assemblies to provide PCB support and/or damping. Potting materials, when used in significant volume or in a volumetrically captive design, create issues with matching coefficients of thermal expansion between materials, resulting in the introduction of mechanical stresses as a result of temperature change. With respect to prior mechanical assemblies, the moving parts tend to wear over time and produce metallic dust that interferes with electronics operation. Other prior approaches include utilizing pads that “float” the PCBs so as to isolate them from housings. These pads can add significant cost to the assembly. Additionally, some prior designs use routings through the PCB in close proximity to sensitive components in order to provide strain relief local to those components.
Generally, prior approaches suffer from one or more of the following disadvantages. Some require hand operated machining for the custom molding of parts to conform to PCB geometry, which is labor intensive, difficult to mass produce, and time consuming. The use of potting materials with high coefficients of thermal expansion can cause issues with PCB assemblies, as discussed above. The use of die-cut or custom foam parts is generally expensive in electronics assemblies. Laminates tend to limit component application to one side of the PCB and/or change industry standard manufacturing processes. Some approaches require non-traditional PCB routings/holes that would be difficult for layout, and mechanical assemblies with moving parts or pre-loaded bonds could fail prior to end-of-life of the product.
Accordingly, a device that reduces or dampens vibrations in PCB assemblies, especially in assemblies mounted in industrial settings, and that does not include the same drawbacks as other prior approaches would be desirable. Embodiments of the present disclosure provide such a vibration dampening device for PCB assemblies. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.